Yep, tires wear out from age alone, no matter how much tread is left.
On a Suzuki Sidekick I drove mostly on back roads, I bought a good looking set of four used tires and ran them for years, though not a lot of miles. The rig is light weight and does not wear tires much, but after 6 or 7 years they started having one flat after another. The tire guy said that they had outlasted their design life and were starting to break down inside, even though there was lots of tread left. Bought a new set, no more flats.
